Directive-reception microphone



Qct. 22, 1929. c, w, HORN 1,732,722

DIRECTIVE RECEPTION MICROPHONE Filed Jan. 2, 1924 2 Sheets-Shee 1 F .1. I8 2 IS ////7////////L\\\\\\\;V///// //K WITNESSES: INVENTOR Charles W Horn.

' ATTORNEY Patented a. 22; 1929 UNITED STATES PATENT OFFICE CHARLES W. HORN, OF SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION. 01E PENNSYLVANIA DIRECTIVE-RECEPTION MICROPHONE Application filed January 2, 1924. Serial No. 688,910.

My invention relates to apparatus for the translation of sound into vibratory electric currents.

Broadly speaking, the object of my inven- 5 tion is to construct a device for-converting sound vibrations into electrical vibrations,

which device shall respond to the sound from A a certain source more readily than to other sounds.

More specifically, the object of my invention is to provide reflecting and shielding -means in connection with a microphone and an attached electrical system which shall ac; cept only sound from a predetermined source and which shall simultaneously reject echoes,

extraneous noises, and reflected sound, thereby giving a much more accurate copy of the original sound waves in a telephone receiver connected to the same electrical system.

A further object of my invention is to provide means incorporated in this s und-selective sound-responsive means whereby the area of space occupied by the source from which sound is accepted can be controlled.

lephony, most of the microphones constructed have been of the type of the simple telephone transmitter suitable for the reception of the voice from a speaker close to the transmitter. Relatively few microphones have been constructed which are suitable for other sounds than speech, or sensitive to sound from a greater distance than a few inches. Because of the lack of such devices, the reception of sound from a group of musical tion and have a small mouthpiece for the collection of the sound of a speakers voice. They were notfound tobe satisfactory for 'culty was experienced in getting suflicient In the development of the prior art of tethisservice. It was found diflicult to. get

sufficient response from such agnicrophone when it was placed more than a short distance from the source of sound. In instances where it was desired to collect sound from a speaker, at a public function, the microphone could not be placed within a few inches of the speakers face, but was required to be hidden. This frequently necessitated placing the microphone a number of feet away from the speaker. Under'these conditions, diffiresponse of the microphone to the speakers voice, and difficulty was also experienced with echoes and extraneous noises which not infrequently covered the speakers voice to such an extent as to make it almost unintelligible.

In the reception of sound by a microphone, it is necessary to distinguish between two types of sound. The sound emanating directly from the source may be called the primary sound, and the echoes and'extraneous sounds including applause and the usual sounds of an audience may be called secondary sound. The purpose of my invention, as before stated, is to obtain maximum response of a microphone to primary sound and a minimum response to secondary sounds.

Other objects and structural details of my invention will be apparent from the followingdescription when read in connection with the accompanying drawings, in which like reference numerals designate corresponding parts and wherein:

Figure 1 is a diagrammatic view, partly in section, of my device as applied to the pick-up of sound from a speaker or soloist.

Fig. 2 is a view showing my invention in section with auxiliary shielding means.

Fig. 3 is a view in perspective of my device, and

Fig. 4 is a polar coordinate curve showing the distribution of sensitivity of response to sounds emanating from sources in various positions. v

Fig. 1 shows a chamber 1 having walls 2. These .walls may have distributed about them reflecting areas 3 capable of developing echoes when sound is produced in the chamber. A soloist or speaker 4 is indicated 100 as producing sound which is received by the device 5 of my invention. An auditor 6 is indicated as applauding.

The device 5 of my invention comprises a parabolic reflector 7, also shown in Fig. 2. The reflector 7 is coated upon its convex surface with a covering of felt, or other fabric, 8, which serves as deadening material to absorb sound impinging upon its rear surface.- A cylindrical shield 9, which is attached to the edge of the reflector 7, is provided as additional shielding means, also covered with felt or other deadening material 10. A microphone 11 is supported substantially at the focus of the reflector 7 by adjustable supporting means 12 comprising a lock nut adjustably movable in a slot in the shielding means 9 and 10.

Conductors 14 are connected to the microphone 11 and to an amplifier 15 which, in turn, is connected by conductors 1G to a radio broadcasting station 20. Signalling and indicating devices 17 and 18 are likewise connected to the various signalling and indicating devices in the chamber and in the broad.- casting station.

In Fig 2, additional shielding means 19 are shown whereby .direct sound waves are prevented from influencing the microphone 11. These shielding means are felt and metal deadening andreflecting devices so shaped as to diffuse the reflected energy.

In the operation of my invention, primary sound from the source 4 enters the aperture of the reflector-7, strikes its reflecting surface and is concentrated by reflection upon the "sensitive element of the microphone 11. In

this way, an optimum amount of sound energy is impressed uponmicrophone 11 from source 4, even though a substantial distance may intervene between the source and the microphone.

The vibratory current of the microphone 11 is then conducted to amplifier 15 from which the amplified vibratory current is conducted to broadcasting apparatus 20 by which it is converted into modulated radiofrequency energy and radiatedinto space.

The increase in sound energy received by microphone 11 issubstantially in the ratio of the projected area of reflector 7 to the projected area of the opening into microphone 11.

By this means, I am able to impress upon microphone 11,.when placed at a distance from the source, an amount of sound energy equivalent to what would; be impressed upon the microphone alone at a very much shorter distance. I am thereby enabled to get a satisfactory response of the microphone without the necessity of placing it close to the sound source.

The greater response ofthe microphone makes less amplification of the vibratory currents necessary to produce satisfactory modulation of the radio sending energy and a stage of amplification in the amplifier 15 may therefore be omitted.

My invention further reduces the influence Sounds emanating from positions in front of said plane and not in the axis of reflector also fail to reach the microphone. Sound which has originated at the desired source and been reflected from a reflecting area, such as shown at 3, may enter reflector 7 through the opening between shield 9 and microphone 11. Such reflected sound, however, strikes the reflector 7 at such an angle as to be reflected out past the microphone 11 and thereby returned to the room and absorbed. As will be obvious, such sound is not reflected into microphone 11 and therefore does not affect it. Likewise, sounds originating from a secondary source, such as an applauding spectator 6, similarly enter the reflector and are reflected out past the microphone 11.

lVhen the microphone 11 is so placed that its sound-responsive element, which may be the center of its diaphragm, is positioned substantially at the focus of reflector 7, sound is received from substantially a point source only, which point source may be quite accurately predetermined. If, however, the microphone 11 is moved away from the focus of the reflector 7, the area of the space Ironi which sound may be received .is greatly broadened. The microphone '11 may be moved either nearer to, or farther from, the reflector 7, but I have found it preferable to move it away from the reflector 7.

By thus changing the position of the microphone 11, it is possible, by my invention, to

collect the sound from substantially a single point source, such as the voice of a soloist, or by the same device, to collect sound from a number of sources, such as several singers, a quartet, a singer and instruments, 0r several instruments. 1

By my invention, as described, I am able to construct a microphone assembly having a directive sensitivity of the character shown in Fig. 4 in which'curve 21 shows the change in response of the microphone 11 tochange in position of source of sounds having avibration frequency of tOOOvibratiors per secend, and curve shows the change in response with change in position to vibrations having a frequency of 120 per second, when the microphone is combined with reflector 7 and the shielding and deadening means described. Because of the greater sharpness of reflection of sounds of short wave length, higher pitched sounds are found to be received with a somewhat greater efliciency and sharpness of directive effect than low pitched sounds, as shown by the curves. These curves show the sharp selectivity of my device for sounds in a particular position with respect to the median line of the reflector and microphone combination of my invention.

By means of this invention, I am able to secure augmented response of a microphone to primary sounds and substantial-reduction of response to secondary sounds, thereby greatly improving theratio of response to primary sounds as compared to response to secondary sounds.

While I have shown only one embodiment of my invention in the accompanying drawings, it is capable of various changes and modifications. without departing from the spirit thereof, and it is desired,v therefore, that only such limitations shall be imposed thereon as are indicatedin the prior art or in the appended claims. I

I claim as my invention:

1. A directive reception microphone comprising a parabolic sound reflector, a soundresponsive element'mounted substantially at the focus thereof, a cylindrical shield surrounding said microphone, and a felt coverj ing upon the exterlor of said reflector and said shield.

2. A directive reception microphone comprising a sound-responsive element and a plurality of surrounding sound-reflective vand sound-absorbent elements, tive elements being adapted to reflect sound from a given source only into said soundresponsive element, said sound-absorbent elements being ada ted toabsorb sound from other sources,

3. The combination with a sound-responsive system comprising a microphone, of

means for excluding extraneous sound from said system, while accepting sound from a desired source, said means comprising a curved reflector, said microphone being placed substantially at the focus of said reflector, a relatively small shielding device placed be tween said microphone and said desired source, a plurality of cylindrical shields surrounding said microphone for reflecting extraneous sounds, and afelt backing for said shields for absorbing extraneous sounds.

4. In a sound pick-up process, the method of increasing the ratio of primary sound to secondary sound which consists in reflecting a beam of primary sound to a concentrated point. and simultaneously reflecting away and shielding out secondary sounds.

into electrical manifestations comprising asound-reception device constituted by a parabolic sound-reflector, a telephone transmitter at substantially the focus of said reflector, a cylindrical shield surounding said telephone transmitter, sound-absorbent means upon the exterior of said reflector and said shield, a chamber wherein a source of sound may be positioned, said sound-reception device being so aligned Withthe position at which said sound-source is to be disposed that the telephone transmitter is intermediate said position and said reflector, and a relatively small shielding device mounted in front of and adjacent to said telephone transmitter, whereby sai transmitter is subjected predominately to sounds coming from a source at said position.

7. A directive sound-reception system comprising a curved sound-reflector, a soundsensitive device disposed substantially at the focus of said reflector, and a relatively small shielding device mounted in front of and adjacent to said sound-sensitive device, whereby said device is mainly influenced by sound waves that are focused thereon by said reflector.

In testimony whereof, I have hereunto subscribed my name this 8th day of December,

c. w. HORN.

one of said reflec- 

